[Illustration:  FIG. 15.—­A small group of Agaricus (Armillaria) melleus.  The toadstool is tawny yellow, and produces white spores; the gills are decurrent, and the stem bears a ring.  The fine hair-like appendages on the pileus should be bolder.]

By the kindness of the forest manager I was allowed to fell one of these trees.  It was chosen at hazard, after the men had struck a large number, to show me how easily the hollow trees could be detected by the sound.  The tree was felled by sawing close to the roots; the interior was hollow for several feet up the stem, and two of the main roots were hollow as far as we could poke canes, and no doubt further.  The dark-colored rotting mass around the hollow was wet and spongy, and consisted of disintegrated wood held together by a mesh work of the rhizomorphs.  Further outward the wood was yellow, with white patches scattered in the yellow matrix, and, again, the rhizomorph strands were seen running in all directions through the mass.

[Illustration:  FIG. 16.—­Sketch of the base of a young tree (s) killed by Agaricus melleus, which has attacked the roots, and developed rhizomorphs at r, and fructifications.  To the right the fructifications have been traced by dissection to the rhizomorph strands which produced them.]

Not to follow this particular case further—­since we are concerned with the general features of the diseases of timber—­I may pass to the consideration of the diagnosis of this disease caused by Agaricus melleus, as contrasted with that due to Trametes radiciperda.

Of course no botanist would confound the fructification of the Trametes with that of the Agaricus; but the fructifications of such fungi only appear at certain seasons, and that of Trametes radiciperda may be underground, and it is important to be able to distinguish such forms in the absence of the fructifications.

The external symptoms of the disease, where young trees are concerned, are similar in both cases.  In a plantation at Freising, in Bavaria, Prof.  Hartig showed me young Weymouth pines (P.  Strobus) attacked and killed by Agaricus melleus.  The leaves turn pale and yellow, and the lower part of the stem—­the so-called “collar”—­begins to die and rot, the cortex above still looking healthy.  So far the symptoms might be those due to the destructive action of other forms of tree-killing fungi.

On uprooting a young pine, killed or badly attacked by the agaric, the roots are found to be matted together with a ball of earth permeated by the resin which has flowed out; this is very pronounced in the case of some pines, less so in others.  On lifting up the scales of the bark, there will be found, not the silky white, delicate mycelium of the Trametes, but probably the dark cord-like rhizomorphs; there may also be flat white rhizomorphs in the young stages, but they are easily distinguished.  These dark